Drywall, invented in 1916 by the USGC, is a labor-saving alternative to plaster. Made mostly of gypsum, it is cheap to produce and can be strengthened with additives like paper, cotton, or fiberglass. Drywall is made by pouring plaster paste onto recycled newspaper paper and then cut into panels and dried in a kiln. It is used in the construction of many homes and can be recycled for use in new drywall or as a component in cement, fertilizer, and soil improver.
What drywall does now, it covers internal structures such as beams and joists and provides a flat surface for paper or paint, once plaster. The plaster, however, took many days to apply and took a long time to dry. In 1916, the United States Gypsum Company (USGC) invented drywall, dried plaster in the form of boards, as an alternative to labor-intensive plastering. The need to build many houses quickly after World War II created a demand for drywall, also called plasterboard or gypsum plasterboard. Drywall made construction much faster and more efficient.
Drywall, made mostly of gypsum, the abundant mineral that makes up plaster, is fairly cheap to produce. After being calcined or fired, gypsum produces a powder that can be mixed with water to form a paste. When the paste dries, it regains the consistency of rock. The resulting plaster is dense enough to support its own weight, but not so hard that it can’t be cut with a knife.
The drywall manufacturer adds pieces of paper, cotton or fiberglass to the plaster powder. Drywall made from these fibers is stronger and less prone to cracking than pure plaster. Starch, which helps paper liners adhere to plaster, also goes into the mix. Once the powder is mixed with water, the addition of a foaming agent introduces air, which will make the boards lighter and easier to use. Drywall made with vermiculite, a naturally occurring mineral, is more resistant to fire than other types of drywall. Other additives include chemicals that are meant to reduce mold.
When the plaster paste is mixed, it is ready to be poured onto the paper. Drywall, made to be painted or otherwise covered, doesn’t have to look pretty, and the paper that lines the drywall comes from recycled newspaper. It comes in two varieties, a light colored card for the front of the cardboard and a gray card for the back. A sheet of paper is spread on a wide conveyor belt which receives the plaster from above. Another sheet is rolled over the plaster layer, and the entire plaster paper sandwich is then pressed down to create the desired panel thickness. Drywall made today comes in several standard thicknesses, each aimed at a particular application.
As the conveyor belt continues to move, this very long board is cut into standard length panels. These panels then roll into a room-sized kiln to be dried. Here the slabs fire at gradually decreasing temperatures until the gypsum core is set. When the boards come out of the drying chamber they are ready to use.
Drywall has made such a difference in how buildings are put together that it is used in the construction of many homes. The utility of drywall makes it plentiful, and its abundance is very evident on the sites of recently demolished buildings. Drywall made unstable by cracking or moisture cannot be repaired, but it can be recycled for use in new drywall. The gypsum in it also has applications as a component in cement, fertilizer and as a soil improver.
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